This invention relates generally to mechanical fasteners, and more particularly to mechanical fasteners having improved physical properties.
Various types of mechanical fasteners are known to the art. Among these are the hook-and-loop type fasteners described in U.S. Pat. No. 4,775,310 (Fischer) and U.S. Pat. No. 4,872,243 (Fischer). Strip-like fasteners of this type, which comprise a large number of closely spaced hook-like projections that releasably engage loops of a companion fastener strip, are currently sold under brand names such as GET-A-GRIP(copyright), Velcro(copyright), and Aplix(copyright).
While these early fasteners had some admirable properties, they also suffered from a number of infirmities. For example, early hook-and-loop type fasteners exhibited notch sensitivity, that is, a pronounced tendency to tear in one or more directions when the base film was notched or nicked by even slight tearing, or by sewing or otherwise securing the fastener to some other product. Typically, the tear would propagate between the rows of hooks.
To reduce notch sensitivity, so-called rip-stops have been integrally molded with the base of some fasteners. Rip-stops are features, typically in the form of humps or bumps, that reduce notch sensitivity by providing localized thickening of the base of the fastener. Rip-stops typically extend between, and are integrally molded with, the hooks in adjacent rows as well as the base. However, while rip-stops may be advantageous in certain applications, they add to the flex modulus, weight and bulk of the overall construction, and also inherently require additional molding provisions and the use of additional materials.
Other methods of reducing notch sensitivity have also been investigated. Thus, U.S. Pat. No. 6,035,498 (Buzzell et al.) discloses the lateral orientation of fastener preforms having discrete fastener elements integral with a base web. The preforms are laterally stretched between 2 and 10 times the width of the original preforms. These products are said to have lateral rip resistance due to the molecular orientation of the film. Moreover, the stretching is said to be capable of reducing the thickness of the base web significantly, depending on the stretch ratio. Thus, the reference notes that, while conventional fasteners have been formed with web thicknesses (between the hooks) of greater than 0.005 inches (0.127 mm), and typically 0.008 inches (0.203 mm) or more, some of the fasteners disclosed in the reference have base film thicknesses of 0.001 to 0.002 inches (0.025 to 0.051 mm). The reference also advocates the use of thermoplastic resins having a flex modulus of at least 150,000 pounds per square inch (1.03 GN/m2) in the constructions described therein, noting that the use of such resins provides higher fastener performance.
However, the approach suggested by Buzzell et al. also has its disadvantages. Because the fasteners disclosed in this reference are stretched laterally, they have significant notch sensitivity in this direction. This is so even if the base film is first oriented longitudinally, followed by lateral stretching. Notch sensitivity in the lateral direction is a substantial detriment in bundling applications, because the propagation of tears in the lateral direction are a common cause of fastener failure in such applications. This is especially true if the items being bundled have sharp edges.
Another problem with earlier hook-and-loop type fasteners was their tendency to cause skin irritation. This problem, which was particularly an issue when these early devices were employed in personal care products such as diapers, sanitary napkins and hospital gowns, was an artifact of the method used to manufacture them. In particular, the methodology commonly used to make hook-and-loop type fasteners often caused the bases of these fasteners to terminate in a stiff, sharp edge. Also, the hook components of these fasteners frequently had an abrasive feel when placed against the skin.
U.S. Pat. No. 5,692,271 (Provost et al.) represents one approach to providing hook and loop type fasteners with a reduced tendency to cause skin irritation. The fasteners disclosed therein have edge margins that are feathered to reduce their thickness and stiffness, which is said to result in a softer, less irritating fastener tape. The product is also provided with rip-stops that are integrally molded with the base and which are offset relative to the hook elements so as to reduce the widthwise stiffness of the product.
U.S. Pat. No. 4,894,060 (Nestegard) represents another approach at reducing the skin irritation associated with the use of mechanical fasteners. This reference discloses a disposable diaper with an improved hook fastener portion (best shown in FIG. 2) whose hooks terminate in a rounded edging. Such a hook, termed a low Profile Extruded Hook (PEH), was designed to have peel and shear values highest in the cross direction as opposed to the machine direction. The individual hooks are formed by notching a ridged preform and then stretching the web in the longitudinal direction.
Profile Extruded Hooks provide excellent holding power on diapers and are resistant to the wearer accidentally (or purposefully) peeling the holding tabs and thus removing the diaper. In addition, the strength of PEH in the lateral direction has been sufficient for diaper tab applications. The reference notes that, as a result of the geometry of these hooks, the hook portions do not have an abrasive feel when they come into contact with the skin. The reference also notes that the hook members are more easily and firmly engaged with many types of loop fastener portions than the hook members on known commercially available hook fastener portions, in large part because they are very small compared to them.
Various methods have also been developed for the production of hook and loop type fasteners, in addition to the methods disclosed in the above noted U.S. Pat. No. 4,775,310 (Fischer) and U.S. Pat. No. 4,872,243 (Fischer). Thus, for example, U.S. Pat. No. 5,260,015 (Kennedy et al.) and U.S. Pat. No. 5,518,795 (Kennedy et al.) describe a method for forming extruded hook fastener strips on a roll equipped with hook-forming cavities in its surface. The strips are formed by extruding a plastic material into the interface between the forming roll and a loop web carried by a backing roll. The loop web is thus firmly bonded to the hook backing on the surface opposite from the hooks.
In spite of the above noted efforts at improving mechanical fasteners and the methods for making them, however, currently existing fasteners still suffer from a number of infirmities. One such infirmity is the stiffness or flex modulus of the overall article and, in particular, of the backing material. Another infirmity is thickness. In particular, most conventional fasteners have relatively stiff (high flex modulus), thick backing materials. For example, as noted above, Buzzell et al. advocates the use in the backing materials of high modulus resins, which would be expected to assume even higher moduli subsequent to the film orientation procedures described therein. This is undesirable for a number of reasons.
First of all, it is difficult to wind a fastener with a high flex modulus backing into a tight radius, as would be required in the bundling of small items (e.g., groups of optical fibers). Even if the fastener is successfully wound into a small radius, the increased bulk usually inherent in higher modulus backings causes the fastener to contribute significantly to the overall diameter of the bundled goods. This is undesirable in many bundling applications such as the bundling of optical fibers, because the bundled item must often be stored in splice enclosures and in other areas where space is at a premium.
Moreover, a high flex modulus contributes to flagging, i.e., the tendency of the fastener to decouple from itself at the terminal end of the mating surfaces. Flagging is especially problematic in the formation of small bundles having small radii, because such applications require the backing to flex the most. In addition to being unsightly, flagging may also compromise the integrity of the mechanical bond achieved with the fastener, and presents a surface which can be snagged, possibly resulting in decoupling. Flagging also presents a cavity in which external contaminants can accumulate, thereby rendering the fastener unsanitary and contributing to a decrease in the integrity of the coupling after repeated uses.
High flex modulus fasteners also conform more poorly to surfaces that they are wrapped around. This makes them more prone to slippage, since less of the fastener surface is in contact with the substrate. Moreover, because the fastener conforms so poorly to the surfaces of the bundled goods, the stress applied to bundled goods by such fasteners will not be evenly distributed. In the case of delicate goods such as optical fibers, this may result in cracking or breaking of the individual fibers or in signal distortion.
Some attempts have been made in the art to produce fasteners using lower modulus materials. These attempts have been largely unsuccessful, however. U.S. Pat. No. 5,692,271 (Provost et al.), for example, which discloses hook type fastener constructions of the general type commonly used in diapers, notes that it is known to reduce the abrasiveness of hook type fasteners by reducing the stiffness or flex modulus of the polymer used to mold the tape used in such fasteners. However, the reference also notes that, in doing so, the hooks become ineffective because they, too, lose their stiffness and hence their ability to secure a garment in place.
Perhaps because of the tendency of hooks to lose some of their holding power with decreasing stiffness, hook and loop type fasteners (which are to be distinguished from hook type fasteners that are devoid of loops) which are currently on the market are relatively thick and stiff, and therefore unsuitable for some applications. Moreover, due to the bulk of these devices, they are more costly on a materials basis than competing products (e.g., twist ties), and hence compete successfully with these products only in high end applications, or where use of such products would damage the goods being tied. Their bulk and thickness also is undesirable for before and during use.
U.S. Pat. No. 6,106,922 (Cejka et al.) describes coextruded fastener constructions in which the fastener is made out of a first and second layer that are joined together while they are still in a molten state. The fastener constructions are of the general type commonly used in diapers, and have a plurality of hooks extending from one or both surfaces of the fasteners. FIG. 5 of that reference depicts an embodiment wherein a lower layer of material forms the base of the fastener and an upper layer forms the surface layer on the base and the entirety of the stem material. Example 11 of the reference describes a fastener having the configuration shown in FIG. 3 of the reference, in which the core portion is formed from an elastic material and the shell portion is formed from a more rigid material. Example 20 of the reference describes a fastener having a 127 micron base film with an ABA structure, in which the middle layer composed of component B is elastic and has a thickness of about 25 microns. While the fasteners described in this reference have many desirable properties, they are made from very soft, low tensile strength materials. Accordingly, they are not well suited for bundling applications and other such end uses where a substantial amount of force is placed on the longitudinal axis of the fastener.
There is thus a need in the art for a mechanical fastener, and in particular a hook and loop type fastener, which is lightweight, strong, thin, and flexible (e.g., has a low flex modulus or degree of stiffness), and whose holding power is as great as, or greater than, the holding power of conventional hook and loop type fasteners. There is also a need in the art for a mechanical fastener having reduced notch sensitivity, especially in the lateral direction. These and other needs are met by the present invention, as hereinafter described.
The present invention provides a new class of fasteners which have reduced notch sensitivity, especially in the lateral direction, and which are lightweight, strong, thin, and flexible (e.g., have a low normalized flex modulus or degree of stiffness), and whose holding power is comparable to or greater than the holding power of conventional hook and loop type fasteners.
In one aspect, the present invention relates to a mechanical fastener, such as a hook and loop type fastener, which is uniaxially oriented in the longitudinal direction. Unlike prior art fasteners which are unoriented, biaxially oriented, or oriented in a lateral direction, the uniaxially oriented fasteners of the present invention exhibit improved tensile strength and reduced flex modulus in the longitudinal direction (due to the thinning of the film attendant to orientation), and improved notch sensitivity in the lateral direction. Because of these properties, the fasteners of the present invention are uniquely suited to provide improved performance in applications such as bundling. In some embodiments of this aspect of the invention, the fasteners may incorporate a laminate of the base film or backing and one or more additional layers that are either unoriented or biaxially oriented before being incorporated into the backing, thereby providing a fastener with improved physical properties for a particular application in both the longitudinal and lateral directions.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein the fastener has a bundle break strength of sbb and a stiffness s, wherein the ratio rsbb/s=sbb/s, and wherein rsbb/s is greater than 477, preferably at least about 500, more preferably at least about 1000, and most preferably at least about 2300.
In yet another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a ratio rw/a defined by the equation rw/a=weight/area, wherein said fastener has a bundle break strength sbb, and wherein the ratio sbb/rw/a is greater than 0.057 (km/s)2, preferably at least about 0.07 (km/s)2, more preferably at least about 0.12 (km/s)2, and most preferably at least about 0.15 (km/s)2.
In yet another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a bundle break strength sbb and a thickness t, and wherein the ratio defined by the equation rsbb/t=sbb/t is at least 28 MN/m2, more preferably at least about 35 MN/M2, and most preferably at least about 46 MN/mr2. In some embodiments, the fastener also has a thickness of less than 1.40 mm, more preferably less than about 1.0 mm, and most preferably less than about 0.90 mm.
In yet another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a bundle break strength sbb and a flagging f, and wherein the ratio defined by the equation rsbb,f=sbb/f is greater than 7.4 MN/m2, preferably at least about 9 MN/m2, more preferably at least about 14 MN/m2, and most preferably at least about 20 MN/m2.
In a further aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a tensile strength st and a stiffness s, wherein the ratio rst/s=st/s, and wherein rst/s is greater than 392, preferably at least about 400, more preferably at least about 1000, and most preferably at least about 1800.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a ratio rw/a defined by the equation rw/a=weight/area, wherein said fastener has a normalized tensile strength st, and wherein the ratio st/rw/a is greater than about 0.058 (km/s)2, preferably greater than about 0.08 (km/s2, more preferably greater than about 0.9 (km/s)2, and most preferably greater than about 0.13 (km/s)2.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a thickness t and a tensile strength st, and wherein the ratio rst/t=st/t is greater than 28 MN/m2, preferably at least about 40 MN/m2, more preferably at least about 50 MN/m2, and most preferably at least about 70 MN/m2, and t is less than about 1.20 mm, more preferably less than about 1.0 mm, and most preferably less than about 90 mm.
In still another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a flagging f and a tensile strength st, and wherein the ratio rst/f=st/f is greater than 6.2 MN/m2, preferably at least about 6.5 MN/m2, more preferably at least about 20 MN/m , and most preferably at least about 50 MN/m2, and t is less than about 1.20 mm, more preferably less than about 1.0 mm, and most preferably less than about 90 mm.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a tensile modulus of mt and a stiffness s, wherein the ratio rmt/s=mt/s is at least about 11000, preferably at least about 14000, more preferably at least about 37000, and most preferably at least about 41000.
In yet another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a ratio rw/a defined by the equation rw/a=weight/area, wherein said fastener has a normalized tensile modulus mt, and wherein the ratio mt/rw/a is greater than 0.46 (km/s)2, preferably at least about 0.6 (km/s)2, more preferably at least about 1 (km/s)2, and most preferably at least about 3 (km/s)2.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a normalized tensile modulus mt and a thickness t, and wherein the ratio rmt/t=mt/t is greater than 0.2 GN/m2, preferably greater than about 0.40 GN/m2, more preferably greater than about 0.7 GN/m2, and most preferably greater than about 1.5 GN/m2, and wherein t is less than 1.40 mm, more preferably less than about 1.0 mm, and most preferably less than about 0.90 mm.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a flagging f and a tensile strength st, and wherein the ratio rst/f=st/f is greater than 48 MN/m2, preferably at least about 50 MN/m2, more preferably at least about 100 MN/m2, and most preferably at least about 1.5 MN/m2.
In still another aspect, the present invention relates to an article comprising a fastener tape which is wound into a roll. The tape may be wound around a spool or other device for ease of production and to give the resulting article greater mechanical integrity. The tape comprises a polymeric substrate which is uniaxially oriented along the longitudinal axis of the tape, and has a plurality of hooks disposed on a surface thereof. The article may also be equipped with a blade for cutting off a portion of the tape, and may be fashioned in the form of a dispenser for the tape.
In another aspect, the present invention relates to a mechanical fastener comprising a substrate and having a plurality of hooks disposed on a first surface of the substrate, wherein said fastener has a low flex modulus mf.
In yet another aspect, the present invention relates to a hook and loop type fastener, wherein said fastener has a thickness t, and wherein t is less than 1.40 mm, preferably less than about 1.20 mm, more preferably less than about 100 mm, and most preferably less than about 90 mm.
In still another aspect, the present invention relates to fastener devices having any combination or subcombination of the above noted aspects, and to methods for using the same.